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Reports back references that will not be resolvable at runtime.
This means that the back reference can never match anything.
A back reference will not be resolvable when the group is defined after the back reference,
or if the group is defined in a different branch of an alternation.
<p><b>Example of a group defined after its back reference:</b></p>
<pre><code>
  \1(abc)
</code></pre>
<p><b>Example of a group and a back reference in different branches:</b></p>
<pre><code>
  a(b)c|(xy)\1z
</code></pre>

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<p><small>New in 2022.1</small>
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